As a radar apparatus that detects azimuth information of a target object in addition to the information of a distance and a speed of the target object, there are disclosed examples of a scan radar apparatus that rotates a radar sensor with a turntable, and detects an angle of arrival of the target object by detecting an angle of the turntable (For example, Patent Document 1).
As a non-mechanical radar apparatus according to a conventional technique, there are disclosed examples of a monopulse radar apparatus that detects an angle of arrival by using a phase-comparison monopulse system. Among the monopulse radar apparatuses, there is a monopulse radar apparatus that detects a target in a wide range and identifies plural targets by utilizing an amplitude change of a reception signal generated by the switching of transmission beams using plural transmission antennas (For example, Patent Document 2).
To secure easiness of size reduction and mass production of antenna units, there is also a monopulse radar apparatus that includes antenna elements disposed in a matrix shape, series power feed lines provided in each row of these antenna elements, and parallel power feed lines that perform parallel power supply in each row of the antenna elements via the series power feed lines (For example, Patent Document 3). According to the monopulse radar apparatus disclosed in the Patent Document 3, array antennas are disposed on the same plane so that all rows or a part of rows within the antenna elements formed in the series power feed lines cross each other at approximately an equal distance, in the two systems of array antennas formed in this way.
Further, there is also a radar apparatus that discloses a technique of preventing an erroneous detection of an azimuth of a target when the target is present in the azimuth in which a phase return occurs (For example, Patent Document 4). A radar apparatus disclosed in the Patent Document 4 compares a first forecast azimuth as a target azimuth calculated from a phase difference of signals received by element antennas disposed at a distance d1 among plural element antennas with a second forecast azimuth as a target azimuth calculated from a phase difference of signals received by element antennas disposed at a distance d2 different from the distance d1. When both forecast azimuths coincide with each other, the radar apparatus employs this azimuth as a detected azimuth.
Patent Document 1: Japanese Patent Application Laid-open No. H10-325863
Patent Document 2: Japanese Patent Application Laid-open No. H11-281729
Patent Document 3: Japanese Patent Application Laid-open No. H9-162626
Patent Document 4: Japanese Patent Application Laid-open No. 2000-230974